This invention relates to an apparatus and a method of controlling an electromagnetic valve that opens or closes an intake and an exhaust valve of an engine by using an electromagnetic coil. A valve activating system has been developed. The system electromagnetically activates an intake and an exhaust valve and electrically controls opening/closing timing for the intake and exhaust valves.
The valve activating system provides a wide range of valve opening/closing timing to achieve appropriate valve opening/closing control in accordance with various engine operating conditions. On the other hand, a noise is produced when an armature hits an electromagnetic coil in each valve mechanism when the valve is accelerated by an electromagnetic coil or a spring. This results in low durability of such valve.
Japanese Patent Laid-Open No. 1996(8)-135416 discloses a control system for decelerating an electromagnetic valve having two solenoids arranged as facing each other. The valve is decelerated so that one of the solenoids which is usually energized while the valve is opened, is temporarily energized while the valve is closed, and the other solenoid which is usually energized while the valve is closed, is temporarily energized while the valve is opened. This system however cannot control valve opening/closing speeds because the speeds are not detected.
The applicant of this invention has filed Japanese Patent Application No. 1996(8)-230094 which discloses a technique for easing a shock produced when a valve sits on a valve seat or when an armature hits a yoke in a valve mechanism by lowering a speed for valve full closing or opening. The deceleration is carried out by temporarily de-energizing an electromagnetic coil for valve opening or closing when the valve reaches a predetermined position for opening or closing, and energizing again the electromagnetic coil when the valve reaches another predetermined position just before valve full closing or opening.
More in detail, as shown in FIG. 1, the Japanese Patent Application No. 1996(8)-230094 teaches that the electromagnetic coil is de-energized when an output of a lift sensor for detecting a position to where the valve is lifted reaches a trigger level VR2, and the electromagnetic coil is energized again when the sensor output reaches another trigger level VR3.
The valve speed after the electromagnetic coil is energized is not necessarily constant, or it sometimes varies in one valve operation cycle as represented by curves "a" and "b" in FIG. 1. The higher the valve speed, the shorter the period of time for the valve being lifted to reach the position corresponding to the trigger level VR3 from the position corresponding to the trigger level VR2. The valve speed is thus cannot be decelerated enough for easing the shock discussed above.